Mechanisms responsible for malignant melanoma progression to highly aggressive brain-metastatic disease remain largely unknown. We have previously demonstrated that certain neurotrophins (NT) and their receptor p75 TR modulate the invasion of melanoma cells to the brain and the activity of an enzyme, called heparanase. This enzyme is a key determinant for the successful degradation of the tumor-surrounding extracellular matrix (ECM): heparanase degrades heparan sulfate proteoglycans (HSPGs), which are important ECM components, at sites within HS linear chains. Our hypothesis is that NT/p75NTR play important roles in melanoma brain invasion and that NT-regulated heparanase is critical in the metastatic melanoma progression being a potential target for antimetastasis drugs. The objective of this application is to determine p75NTR function as a molecular determinant of brain metastases formation and the role of heparanase in invasion and angiogenesis. We selected melanoma cells with low/high p75NTR expression and generated a monoclonal antibody against human heparanase that inhibits its enzymatic activity and experimental metastases formation. In addition, we have access to the recently cloned human heparanase, related probes, and novel important enzyme inhibitors. Our specific aims are: 1. To define p75NTR as a molecular determinant of brain-metastatic melanoma cells, which will be accomplished by modifying p75NTR gene expression and analysis of p75NTR variants for their organ colonizing abilities in nude mice, in particular to the brain. 2. To characterize NT-regulated heparanase gene expression at specific steps of metastasis in malignant melanoma, which will be accomplished by studying the distribution and mechanisms of human heparanase to test the precise function of heparanase in the multistep process of melanoma metastasis. 3. To determine the role of heparanase in angiogenesis, which will be accomplished by relating angiogenic molecules and models to heparanase functionality by using purified enzyme and HS substrates subpopulations from corresponding HSPGs. We anticipate that the results of our proposed research will fundamentally advance the field of brain tumors biology and metastatic ECM processing. Of significance, they are expected to provide new targets for preventive and therapeutic interventions that will be particularly important to the growing numbers of persons who have malignant melanoma, and are experiencing the "urgency" of the melanoma problem.